1. Field of the Invention
The present invention relates to a method of transporting substrates including a semiconductor substrate, a glass substrate for a liquid crystal device and the like in a substrate processing apparatus including a plurality of processing units each for performing a predetermined process on these substrates.
2. Description of the Background Art
In a substrate processing apparatus which performs various processes on semiconductor substrates (or wafers), glass substrates and the like in the process steps of manufacturing semiconductor devices, liquid crystal devices and the like, attempts have been made at a multi-unit structure in which there are provided a plurality of processing units all responsible for a single process step and at a hybrid structure in which there are provided different types of processing units for performing a succession of different process steps in a single apparatus, thereby to respond to a request of manufacturers for improvement in throughput. The improvement in throughput, however, is not achieved only by such hybrid arrangement, but significantly depends on how efficiently to operate the processing units.
In general, such a substrate processing apparatus performs a process on a series of lots in accordance with a predetermined process flow, and thereafter performs the process on the subsequent lots. There may be situations where a processing unit not included in the process flow is completely out of operation, depending on the details of the process flow. To better the situations, a technique has been known, for example, in which a process in a preceding process flow is interrupted by the execution of a process in another process flow not competing with the preceding process flow. Such a technique is disclosed, for example, in Japanese Patent Application Laid-Open No. 7-283094 (1995).
The control algorithm in the method disclosed in Japanese Patent Application Laid-Open No. 7-283094 (1995) increases in complexity as the substrate processing apparatus increases in size. It is therefore difficult to achieve high efficiency while maintaining the reliability of processing. Further, the interrupt process depends on the details of the preceding process flow, and is limited in executability. There arise another problem in that installation of an additional processing unit requires the construction of a new process flow.